Controllable hydrophobization of sands with self-healing polymeric microcapsules

Rui Qi, Hongjie Lin, Sergio Lourenco, Antonios Kanellopoulos

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Hydrophobized soils have functional hydrophobic coatings to delay or restrict water infiltration and thus prevent infrastructure failure and long-term degradation. Over time, hydrophobized soils will be subjected to degradation under the action of external stresses, leading to the loss of its functional properties. Microencapsulation approaches, initially developed for self-healing applications emerge as a potential solution to enhance, switch (from hydrophilic) or prolong the longevity of hydrophobized soils. The aim of this study is to produce and investigate the effectiveness of microencapsulation to impart hydrophobicity in granular materials in response to external stimuli. In this research, polydimethylsiloxane (PDMS), with hydrophobic properties, is encapsulated in calcium alginate microcapsules with the ionic gelation method. The effectiveness of the microcapsules to induce hydrophobicity is investigated by mixing sand with micro capsules and quantifying the change of the contact angle and water drop penetration time (measures of hydrophobicity) under an external trigger, i.e., under drying and consecutive wetting–drying cycles. The results show that microcapsules
release the hydrophobic cargo (PDMS) during shrinkage. After drying, the PDMS content in sand increased to 0.1–0.8% by
mass of sand. The released hydrophobic cargo (PDMS) induced hydrophobicity in sands, reflected by a contact angle
increase from 29.7° to at least 87.7°. The amount of polydimethylsiloxane encapsulated is a key parameter controlling the
release of hydrophobic cargo. In addition, 4% capsule content in sands is identified as an effective microcapsule content in
inducing hydrophobicity.
Original languageEnglish
Number of pages16
JournalActa Geotechnica
Publication statusPublished - 18 May 2024


  • Microcapsules
  • Hydrophobicity
  • Self-healing
  • Sand
  • Soils
  • Sands
  • Release behavior
  • Calcium alginate
  • Polydimethylsiloxane


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